Semiconductor lasers or laser diodes have many advantages as compared to other types of lasers, such as solid-state, gas, or liquid lasers. Included among these advantages are the potential to be manufactured in high volume and at relatively low cost. Further, semiconductor lasers have electrical current requirements compatible with conventional semiconductor circuitry; and high voltage supplies or flash tubes are not required for operation of semiconductor lasers.
Gallium Arsenide (GaAs) is the semiconductor commonly used in the manufacture of semiconductor lasers, and the so-called Fabry-Perot cavity or interferometer is the commonly used resonant cavity in such lasers. A resonant cavity is a chamber having a size which reinforces energy injected therein at the natural frequency as determined by the chamber's dimensions. The resonant cavity is required in a semiconductor laser to provide positive feedback and quantum amplification. The Fabry-Perot cavity has a pair of perfectly aligned parallel mirror planes which are obtained by cleaving or polishing.
Semiconductor lasers, such as the Fabry-Perot type, are typically fabricated from a wafer, such as a heteroepitaxial wafer, which is cleaved into a plurality of parallel strips. These strips are referred to as laser bars. Each laser bar is subsequently diced into individual generally rectangular laser diodes. A typical laser diode may have a width of approximately 300 .mu.m and a length of approximately 250-750 .mu.m. Further, the specific quantity of laser diodes per each laser bar can vary considerably. For example, there can be anywhere between 32 and 64 laser diodes per laser bar. After dicing of the laser bar, each individual laser diode is appropriately packaged for implementation in an electronic device requiring such a diode.
Testing of each laser diode for proper operation before implementation in an electronic device is an important aspect of manufacturing. Specifically, the electrical and optical properties of each laser diode must be tested.
Conventionally, testing of laser diodes is conducted either after packaging of each individual diode or before packaging but after dicing of the laser bar into individual laser diodes. Testing after packaging is undesirable since a considerable amount of packaging time, packaging effort and packaging material is needlessly expended if it is ultimately determined that the laser diode is functioning improperly.
Testing before packaging but after dicing is also undesirable because use of existing test methods and equipment can be time consuming and frequently results in damage to the diodes. In this regard, each diode must be individually probed during testing. Typically, a tester employing a single probe is used to test individual laser diodes. Such testers are capable of probing and testing only one diode at a time, and thus such a testing scheme is inefficient and impractical, particularly when testing large quantities of diodes.
Further, laser diodes commonly utilize relatively soft metal contacts, such as gold contacts, for connecting to other components. These soft metal contacts are the contact points of the diodes that must be probed during testing. Probes employed in standard testers generally have sharp points and comprise relatively hard metal, such as barium copper, stainless steel, or the like. Frequently, these probes "dig" into the soft metal contacts of the diodes, thus causing extensive and irreparable damage to the contacts.
Another scheme proposed testing each laser diode before dicing the laser bar into individual diodes. Unfortunately, standard single probe testers require time consuming, inefficient and complicated indexing of the test probe to each diode of the laser bar in order to conduct the required tests. Although multiprobe type testers solve the indexing problems associated with single probe testers, it has proven difficult to manufacture a tester having a series of accurately and precisely spaced apart probes which correspond to the closely spaced apart contacts between adjacent diodes of a laser bar. In this regard, the distance between the contact of each diode on a laser bar may be on the order of approximately 300 .mu.m or less. Moreover, the aforementioned problem of damaging the diode contacts still exists in these single probe and multiprobe testers used for testing before dicing of the laser bar.